Reciprocal Roof Frame Building: How-To, Materials, and Supplies

Earlier this year, I was introduced to the concept of a so-called “reciprocal roof frame”. After hearing about the concept from a friend, we later browsed the internet in search of natural buildings featuring this mysterious design. When I finally saw examples of different reciprocal roofs, I was immediately enamored: here was a roof structure so totally simple, strong, and above all, beautiful.

A reciprocal roof is a self-supporting, round structure composed of interlocking beams that equally bear the weight of one another. Composed of as few as three beams, a reciprocal roof can incorporate practically any number of beams and span great distances while still maintaining its integrity. Best suited to round structures, this style of frame is incredibly strong, and “twists upon itself rather than spreading apart”, when pressure is applied from above. Notably, it is an appropriate frame for living roofs, because of its strength. The reciprocal roof is a glorious design for green buildings.

The history of the reciprocal roof seems clouded due to a lack of comprehensive information (a Google search for “reciprocal roof” or related terms will result in only a handful of actual buildings featuring the design, plus some other minimal historical information), but from what I gather, it was designed by Graham Brown in 1987, when the idea came to him from “out of nowhere” (which is also the name of his company).

History aside, the reciprocal roof is also incredibly simple to build, and very appropriate for amateur green builders, and it is perfect for roundhouses and circular structures. It is perhaps most famously featured in the phenomenal low-impact woodland home of Simon Dale (see right), and Tony Wrench’s roundhouse in Wales, two well-known natural buildings in Europe.

How to build a reciprocal roof

There exists an overall dearth of how-to information on the construction of the reciprocal roof, although there is at least one comprehensive resource for aspiring reciprocal roofers. Tony Wrench’s Building a Low-Impact Roundhouse features fairly complete instructions for building a frame, including plenty of photos and sketches to illustrate the process. Other than Earthbag Building by Kaki Hunter and Donald Kiffmeyer, which features a mere paragraph on reciprocal roofs, this is the only published resource. It is a good one and worth tracking down.

My experience building a reciprocal roof frame

Very recently, I had the pleasure of constructing my very own reciprocal roof for a small cob house that I am building (see above). It took two attempts (only because the poles of the first frame were a little lacking, in terms of diameter), but it was a very simple process, and one I would gladly repeat. My own frame is composed of 28 total poles, hand-cut from nearby land, including fourteen primary black locust rafters, and another fourteen secondary rafters that are not tied into the main frame. Eventually, this roof will be covered with an impermeable membrane and become a living roof.

Ultimately, I hope others will learn about and experience the simplicity and beauty of the reciprocal roof frame. It is truly an ingenious design, and perfect for round natural buildings.

Reciprocal roof resources

Here is an assembly of links that I have found useful in my pursuit of the reciprocal roof:

Tony Wrench’s website has some photos and information about his living reciprocal roof

The LessPress Snail Cabin has a reciprocal roof made with dimensional lumber. Also, be sure to check out their Excel spreadsheet for calculating beam lengths and positions for both circular buildings and otherwise

For math nerds, visit The Pavilion for a very technical description of how reciprocal roofs function

Zone5 has a brief description with some images of a Tony Wrench-style reciprocal roof construction for a roundhouse here and here

Check out a scale reciprocal roof model and design using dimensional lumber at Casa de Baro

Cae Mabon in Snowdonia of North Wales features several buildings with reciprocal roofs. Images here.

Design Forward has a very brief snippet about the history of the reciprocal roof design

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About the Author

ziggy I'm a 26-year-old currently living at Dancing Rabbit Ecovillage in northeast Missouri, an intentional community devoted to sustainable living and culture change. Things you might find me doing here (other than blogging) are building with natural materials, gardening, beekeeping, making cheese, candlemaking, and above all else, living simply.
You can read about my on-going natural building projects at: http://www.small-scale.net/yearofmud

“The third type of construction that will yield an arch shaped roof is a Lamella (a. k. a. Summerbell) roof, in which the truss construction is replaced by an “eggcrate” style interconnecting series of 2 X materials, which forms the support for the sheathing. The outward (lateral) thrust created on the walls is resisted by tie rods and turnbuckles. Hence, this style of roof construction has the same limitations as the true bowstring truss roof. However, with one exception (S. E. corner of Third and Alamitos), since it lacks the hip sections it cannot be easily cross-ventilated. ”

“The third type of construction that will yield an arch shaped roof is a Lamella (a. k. a. Summerbell) roof, in which the truss construction is replaced by an “eggcrate” style interconnecting series of 2 X materials, which forms the support for the sheathing. The outward (lateral) thrust created on the walls is resisted by tie rods and turnbuckles. Hence, this style of roof construction has the same limitations as the true bowstring truss roof. However, with one exception (S. E. corner of Third and Alamitos), since it lacks the hip sections it cannot be easily cross-ventilated. ”

this is beautiful and i’m eager to experiment with it. all the examples I’ve seen of this technique employ a living roof though. that isn’t practical for my application (arid climate and small diameter poles). any thoughts on alternative roofing material for this frame?

galen

this is beautiful and i’m eager to experiment with it. all the examples I’ve seen of this technique employ a living roof though. that isn’t practical for my application (arid climate and small diameter poles). any thoughts on alternative roofing material for this frame?

Wow this is really new to me and you are right. There aint a lot of information about reciprocal roofs on the web. This is truly a green building structure. With this roofing, I think we don’t need to be in the woodland coz maybe we can try building a small round house with this roof and make it a great addition to our place.

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